Initially, the early slide projectors were fed one slide at a time. Subsequent improvements led to a cross-feed system in which the slides were fed from either side of the projector. Automatic cross-feeds for stacked slides was the next development in the projector art. Later on, magazines or cassette feeds were used to provide a slide storage system which operated in conjunction with the projector.
At the present time slides are stored in carousel trays or linear magazines, disposed either horizontally or vertically in the projector, in rectangular slide trays or in cubes. In each one of these storage systems, the slide has to be removed from its holder in order to preview or otherwise inspect the slide.
A system for previewing all of the slides of a set simultaneously is disclosed in U.S. Pat. No. 4,133,605 and comprises a rectangular light table having a substantially horizontal translucent surface illuminated by a projection bulb controlled by a shutter, which in one position allows a projection beam to be directed through a central transparent window in the surface and through a slide in registration therewith and above which there is positioned a lens and mirror assembly held by an arm mounted on a side of the light table for the projection of the image on the slide. The slide is one of several in a planar array held in a slide holder, the holder being moved across the surface to align different slides with the window, the surface being larger than the holder so that the entire slide holder always remains on the surface.
In another embodiment of this disclosure, the illuminated surface is arranged vertically on a base, with a projector lamp mounted on the base on one side of the surface and directing a light beam through the center thereof, where the light beam is received by a lens assembly mounted on the base on the other side of the illuminated surface in alignment with the projector lamp, whereby a slide interposed in the light beam is projected. As in the first embodiment, the illuminated surface is substantially larger than the slide holder.
Disadvantages associated with the first embodiment of the prior art relate to to the size of the light table being substantially larger than the slide holder, and further exaggerated by the arm mounted on the side of the table which holds the mirror and lens assembly, and the slide holder support mounted on the opposite side of the table. In addition, the table surface being substantially horizontal requires that the projectionist be standing in order to preview the slides. Still further, the single light source controlled by a shutter for both projection and illumination of the slides presents an added complexity.
Further disadvantages associated with the second embodiment of the prior art are again related to the illuminated surface being substantially larger than the slide holder and unitary with the base, making it difficult to transport the projection system.